1. Field of the Invention
The present invention relates to an HDMI (High Definition Multimedia Interface) system, and more particularly, to a method for setting mute flag in connection with transmission of audio data and auxiliary data transmitted through HDMI system, and an HDMI system using the same method.
2. Description of the Related Art
HDMI is a standard for connecting a source device which sends data and a sink device which receives data, wherein the source device may be, for example, set-top box or DVD player and the sink device may be, for example, digital TV.
General architecture of HDMI system is suggested in “HDMI specification version 1.2a, FIG. 3-1 HDMI Block diagram”, which is incorporated herewith as FIG. 1. Referring to FIG. 1 of the present invention, an HDMI system consists of a source device 100 which sends data and a sink device 200 which receives data. Each of source device and sink device may have more than one HDMI inputs and HDMI outputs. All the HDMI inputs at the source device and the sink device conform to the specification for the HDMI sink device, and all the HDMI outputs at the HDMI system conform to the specification the for HDMI source device.
As shown in FIG. 1, HDMI cable 300 employed in HDMI system holds four different channels, each of which consists of TDMS (Transition Minimized Differential Signaling) data channels 301, 302, 303 and clock channel 304. These channels are used for transmitting video data, audio data and auxiliary data. Also, HDMI system holds VESA (Video Electronics Standards Association) DDC (Display Data Channel) 400, which is used for exchanging configuration and status information between the single source device and the single sink device. Alternatively, HDMI system may use CEC (Consumer Electronics Control) line 500 which transmits CEC protocol to provide high level control among various viewing devices in user environment.
As described above, audio data, video data and auxiliary data are transmitted from HDMI sender 101 of the source device 100 to HDMI receiver 201 of the sink device 200 through three TMDS (Transition Minimized Differential Signaling) data channels 301, 302, 303 and video pixel clock is transmitted through TMDS clock channel 304. The video pixel clock is used as frequency standard for restoring data on three TMDS data channel 301, 302, 303 by receiver 201 of sink device 202.
The difference between traditional DVI (Digital Visual Interface) system and HDMI system is that audio data and auxiliary data as well as video data are transmitted through HDMI cable 300. Video data is transmitted as a series of 24 bit pixel on the three TMDS data channels and HDMI system employs packet structure for transmitting audio data and auxiliary data.
There is a packet type called General Control packet in HDMI specification version 1.2a (see table 3). The General Control packet was introduced in HDMI specification for muting audio and video signal simultaneously to reduce transient impacts between the source device and the sink device.
The General Control packet retains Clear_AVMUTE flag and Set_AVMUTE flag for muting or for releasing the muting of audio and video signal simultaneously. It is optional for the source device to send muting signal, but is required for the sink device to receive the signal for muting signal. Further, it is optional for the sink device to effectively process the received muting signal.
The reason HDMI system employs these mute flags are to minimize the transient impacts due to the status changes when the source device sends signals to the sink device. For example, it is possible to prevent audio pop noise which may occur in the source device by setting the AVMUTE flags.
When Set-AVMUTE flag is set in the source device, the sink device receives invalid video or audio signal. Accordingly, HDMI sink device can optionally perform the muting of video or audio signal as required.
Recently, most of home appliances are equipped with HDMI input/output terminals. Also, many high level functions (e.g. memory card operability) are increasingly added to set-top boxes or DVD players which meet the HDMI specification. Accordingly, the interoperability between the various source devices and the sink devices becomes an important issue.
More specifically, during transient period when resolution or frequency is being changed between the source device and the sink device, there may occur flickering or noise (hereinafter transient impacts). To prevent the transient impact, a technology to reduce transient impact of devices employing HDMI specification, or a technology to increase interoperability between devices is required.
The mute flags retained in the General Control packet of HDMI specification could be a solution to increase the interoperability between the source device and the sink device. Meanwhile, sometimes it is enough to simultaneously set Clear_AVMUTE flag and Set_AVflag to mute or release muting both audio signal and video signal (e.g. when the resolution is being changed), but at other times it is required to mute or release muting one of audio signal and video signal. For example, when playing back MP3 file from memory card which was added as a high level function or when changing frequency of MP3 file, more detailed control to selectively mute or release muting one of audio or video signal is desirable rather than to mute or release muting both of them. The need for more detailed control is increasing according to the high-end trend and diversification of source device and sink device.